No, it's not wrong that you are dating him. He probably doesn't want your brother to know because he thinks your brother will be angry with him. Brothers tend to be protective over their sisters.
Is it wrong that I am dating my brother's best friend? For some reason, he doesn't want my brother to find out..
No .
Hi Mary,
of course is not! As long as you two guys like each other and are happy together, why would it be wrong?
The fact that he doesn't want to talk about it with your brother though seems a bit understanding: He might be scared about his reaction and about what he might think. Some friendships are challenged because of this kind of situations, so he might want to take things slowly.
Talk to him and maybe ask him why, and see if you can sort it out. You can take things slowly, and you might decide to talk with your brother and see how it goes. It's good not to rush things but it isn't a good thing to hide away for too long because your brother might find out sooner or later and it is not a pleasant thing.
Plus, it isn't great to have a relationship where you have to hide things and feelings away. Just take your time but make sure that you and your boyfriend work together to make things develop. Hope it works out for both of you!